Overview

The SQLAlchemy SQL Toolkit and Object Relational Mapperis a comprehensive set of tools for working withdatabases and Python. It has several distinct areas offunctionality which can be used individually or combinedtogether. Its major components are illustrated below,with component dependencies organized into layers:_images/sqla_arch_small.pngAbove, the two most significant front-facing portions ofSQLAlchemy are the Object Relational Mapper and theSQL Expression Language. SQL Expressions can be usedindependently of the ORM. When using the ORM, the SQLExpression language remains part of the public facing APIas it is used within object-relational configurations andqueries.

Documentation Overview

The documentation is separated into three sections: SQLAlchemy ORM,SQLAlchemy Core, and Dialects.

In SQLAlchemy ORM, the Object Relational Mapper is introduced and fullydescribed. New users should begin with the Object Relational Tutorial. If youwant to work with higher-level SQL which is constructed automatically for you,as well as management of Python objects, proceed to this tutorial.

In SQLAlchemy Core, the breadth of SQLAlchemy’s SQL and databaseintegration and description services are documented, the core of which is theSQL Expression language. The SQL Expression Language is a toolkit all its own,independent of the ORM package, which can be used to construct manipulable SQLexpressions which can be programmatically constructed, modified, and executed,returning cursor-like result sets. In contrast to the ORM’s domain-centricmode of usage, the expression language provides a schema-centric usageparadigm. New users should begin here with SQL Expression Language Tutorial.SQLAlchemy engine, connection, and pooling services are also described inSQLAlchemy Core.

In Dialects, reference documentation for all provideddatabase and DBAPI backends is provided.

Code Examples

Working code examples, mostly regarding the ORM, are included in theSQLAlchemy distribution. A description of all the included exampleapplications is at ORM Examples.

There is also a wide variety of examples involving both core SQLAlchemyconstructs as well as the ORM on the wiki. SeeTheatrum Chemicum.

Installation Guide

Supported Platforms

SQLAlchemy has been tested against the following platforms:

  • cPython 2.7

  • cPython 3.4 and higher

  • PyPy 2.1 or greater

Changed in version 1.2: Python 2.7 is now the minimum Python version supported.

Changed in version 1.3: Within the Python 3 series, 3.4 is now the minimum Python 3 version supported.

Platforms that don’t currently have support include Jython and IronPython.Jython has been supported in the past and may be supported in futurereleases as well, depending on the state of Jython itself.

Supported Installation Methods

SQLAlchemy installation is via standard Python methodologies that arebased on setuptools, eitherby referring to setup.py directly or by usingpip or other setuptools-compatibleapproaches.

Changed in version 1.1: setuptools is now required by the setup.py file;plain distutils installs are no longer supported.

Install via pip

When pip is available, the distribution can bedownloaded from PyPI and installed in one step:

  1. pip install SQLAlchemy

This command will download the latest released version of SQLAlchemy from the PythonCheese Shop and install it to your system.

In order to install the latest prerelease version, such as 1.3.0b1,pip requires that the —pre flag be used:

  1. pip install --pre SQLAlchemy

Where above, if the most recent version is a prerelease, it will be installedinstead of the latest released version.

Installing using setup.py

Otherwise, you can install from the distribution using the setup.py script:

  1. python setup.py install

Installing the C Extensions

SQLAlchemy includes C extensions which provide an extra speed boost fordealing with result sets. The extensions are supported on both the 2.xxand 3.xx series of cPython.

setup.py will automatically build the extensions if an appropriate platform isdetected. If the build of the C extensions fails due to a missing compiler orother issue, the setup process will output a warning message and re-run thebuild without the C extensions upon completion, reporting final status.

To run the build/install without even attempting to compile the C extensions,the DISABLE_SQLALCHEMY_CEXT environment variable may be specified. Theuse case for this is either for special testing circumstances, or in the rarecase of compatibility/build issues not overcome by the usual “rebuild”mechanism:

  1. export DISABLE_SQLALCHEMY_CEXT=1; python setup.py install

Changed in version 1.1: The legacy —without-cextensions flag has beenremoved from the installer as it relies on deprecated features ofsetuptools.

Installing a Database API

SQLAlchemy is designed to operate with a DBAPI implementation built for aparticular database, and includes support for the most popular databases.The individual database sections in Dialects enumeratethe available DBAPIs for each database, including external links.

Checking the Installed SQLAlchemy Version

This documentation covers SQLAlchemy version 1.3. If you’re working on asystem that already has SQLAlchemy installed, check the version from yourPython prompt like this:

  1. >>> import sqlalchemy
  2. >>> sqlalchemy.__version__ 
  3. 1.3.0

1.2 to 1.3 Migration

Notes on what’s changed from 1.2 to 1.3 is available here at What’s New in SQLAlchemy 1.3?.